Current monitoring systems use a combination of passive infrared detectors and optical cameras to monitor areas. Infrared sensors detect heat signatures, which can be used among other things to trigger an alarm when an object emanating heat is detected. Cameras can also be used to trigger an alarm if enough pixels change to identify a foreign object.
Lighting changes, however, can cause false detections by a camera and consequently false alarms. Hot ambient temperatures can cause an infrared detector to not detect an animal or person in its field of detection.